Public health researchers are still trying to understand the effects of the Affordable Care Act even as the Republican-controlled Congress and White House plot how to dismantle the law, also known as Obamacare.

A new study published today in Health Affairs shows that the Affordable Care Act's Medicaid expansion not only increased insurance coverage rates but also improved access and affordability among low-income patients over the last three years. The study's findings come out at a critical time as the Senate works on passing its version of the AHCA, which could change Medicaid, insurance premiums and a number of other aspects of the healthcare system.

"This is a critical time in both national policy conversations with what happens in Congress as well as what happens at the state level," said Benjamin Sommers, lead author and an associate professor of health policy and economics at the Harvard T.H. Chan School of Public Health.

Sommers and the other co-authors had a research firm perform random telephone surveys from 2013 -- the year before the Affordable Care Act went into effect -- to 2016. They spoke to a total of 10,885 people between 19 to 64 with income levels below 138 percent of the federal poverty line, the Medicaid expansion coverage threshold.

The researchers collected responses from low-income people in three states: Kentucky, which expanded Medicaid; Arkansas, which expanded private insurance in the federal Marketplace; and Texas, which opted for no expansion.

Survey respondents answered whether they had insurance as well as many other factors, such as if they had gaps in coverage, difficulty seeing doctors, trouble affording co-pays and medications, and adequate preventive care. They were also asked to rate their own health.

All three states included in this study had similar rates of uninsurance - around 40 percent - before the ACA. By 2016 the uninsurance rate dropped to 7.4 percent in Kentucky and 11.7 percent in Arkansas while plateauing at 28.2 percent in Texas.

Cost and quality of care also improved Kentucky and Arkanasa, where patients were 41 percent more likely to have a regular source of care, spent $337 less out of pocket annually, and were nearly 23 percent more likely to rate themselves as being in "excellent" health.

Sommers said this study joins a growing body of evidence that the ACA helped many people to better afford primary care and preventative healthcare. An estimated 20 million Americans have gained health care coverage after the ACA was passed in 2010.

"In broad brushstrokes it's reasonable to assume this is similar to what's happening for people gaining insurance across the country," Sommers said.

Christine Eibner, a senior economist and professor at the Pardee Rand Graduate School, said the study was interesting and gave better context about the impact of the ACA compared to past research.

"What makes it unique is that it examined a broader set of outcomes than simply change in insurance: affordability, self-reported health status, use of preventive services, measures of access to care, and measures of quality," she told ABC News.

More than half of the participants said they had preexisting conditions, and the ones living in Medicaid expansion states were more likely to have a regular source of care for their chronic condition, with fewer delays in care and less trouble paying medical bills.

With the AHCA currently in the Senate, it remains unclear how healthcare in the U.S. could change. But Sommers points out that the data reinforces the idea that diminishing healthcare coverage can have very real consequences on overall health.

"There's a question of whether these benefits are worth the cost -- and that conversation is worth having -- but policymakers should not imply that taking coverage away doesn't have consequences," he said.